Stupid EBD / ABS questions
 

So, I'm looking into a pedal set and stuff for my burnt out BRZ chassis.

The entire wiring harness is toast as are all of the ABS / EBD / whatever components, AND I'm not going to have ABS tone rings anyway because of suspension swapping and such. So any kind of ABS is very out of the question.

That said, is it possible to run new lines to the brakes for a traditional braking setup with a prop valve going to the rear, while retaining the stock master cylinder? Would I even want to? I know an aftermarket pedalbox with tandem masters is "better", but I'll be driving the car on the street occasionally and I'd prefer to keep the vacuum assist.

Does anyone know if the stock MC is 15/16", 1", or 1-1/16"? I assume it's either 1" or 1-1/16" considering people claim STi brembos work fine with the stock master. I'll likely be running something similar to STi brembos or the AP sprint kit.

Does the factory master even have the correct ports for something like this? I see it's got two lines, one on the front and one on the side. Is that an output to the ABS pump and a return, or is it a front and a rear? I have no idea how EBD works.

Maybe I should just try and fit an Impreza booster and master from a pre-EBD car?

Yes, you can run new lines for a more traditional braking set up with the stock master cylinder, no issue. You would need to buy an adjustable hydraulic proportional valve such as this one.

http://www.speedwaymotors.com/Wilwoo...ock,41747.html

In its normal configuration both lines feed pressure from the master cylinder into the ABS unit. There are two lines for redundancy in case a brake line fails. Inside the master cylinder there are two cylinders independently applying pressure to each of those lines. They are titled brake circuit one and brake circuit two. In this vehicle each line goes to both one front wheel and one rear wheel. For example BC1 would power the FR and RL and BC2 would power FL and RR or vice versa. This configuration is known as a x-split and it prevents the vehicle from inducing excessive yaw during a brake circuit failure while maintaining the stopping power of one of the front wheels. There is no dedicated return line from the abs unit to the master cylinder. The fluid flows from the master to the abs unit during brake applies and flows back to the master cylinder during brake releases. During ABS the MC is isolated from the calipers and the ABS pump cycles fluid from the wheels back to input side of the ABS unit.

EBD uses the ABS unit to limit pressure in the rear wheels during hard applies. In an EBD equipped vehicle all four brakes have equal pressure until a programmed threshold is reached based on vehicle state. When EBD is active the rear wheels are isolated from the brake system and the last brake pressure achieved prior to the EBD event is maintained on the rear wheels initially. If the vehicle state changes EBD can further decrease rear wheel pressure or enter ABS depending on wheel slip.

Without the ABS unit you will no longer have ABS, EBD, TCS, VDC, vehicle speed on the dash or an odometer. The electric power steering likely also uses wheel speed to determine assist level. Without the ABS unit the power steering unit will default to some type of backup mode and will likely result in excessive steering assist. I can't think of anything else off the top of my head but any vehicle system that uses wheel speed or vehicle acceleration will only function in backup mode which will affect its behavior. You will also have a permanently illuminated dash light warning you of the situation.

You shouldn't need to do this, the existing MC and Booster should be fine. However, if you are changing the calipers to something much larger you must ensure the MC can move adequate fluid volume to achieve the necessary wheel pressure. This is true of any vehicle however, with or without an ABS unit.